1. Field of the Invention
The invention relates to a mixer assembly and also to a method for mixing and producing a fuel-air mixture which is fed to a burner system for operating a heat engine, especially a gas turbine plant.
2. Brief Description of the Related Art
For the operation of high-performance heat engines, especially gas turbine installations, there are high requirements with regard to the production and making available of an ignitable fuel-air mixture which is mixed through as homogenously as possible, by means of the combustion of which fuel-air mixture inside a combustion chamber hot gases are formed which serve for driving turbine stages, by means of which a generator is ultimately driven for electrical power production.
In order to carry out the combustion process as efficiently as possible, and, furthermore, to make sure that all of the fuel which is mixed with air is combusted, it is necessary to feed to the burner system a homogenously mixed fuel-air mixture in the form of a mixture flow which has a largely equally distributed velocity profile along the total flow cross section.
It is obvious that to similarly increase the demands which are to be made on the mixer assemblies by the increase in performance of modern heat engines, it is necessary to make available ever greater amounts of fuel-air mixtures, particularly as the swallowing capacity of such modern plants becomes continually greater. Also, the aspect of the increasing overall size and complexity, especially in modern high performance gas turbine plants, plays an important role in the design of required mixer assemblies. Therefore, it is necessary to form the mixer assembly as flexibly as possible on a large scale so as not to have to provide a specially adapted mixer design for each individual gas turbine plant which is formed with a different power output.
In particular, the use of so-called catalytic burner systems, which are used increasingly in high-performance gas turbine plants especially for reasons of avoiding pollutant emissions, require a large mass flow of fuel-air mixture which mixes as homogenously as possible and which is to have an uniformly distributed velocity profile along the total flow cross section before entry into the catalyst unit.
To date, only unsatisfactory solutions for mixing and making available such fuel-air mixtures are known, as they are gatherable, for example, from an article by R. L. Hack et al., “Design and Testing of a Unique, Compact Gas Turbine Catalytic Combustor Premixer”, Proceedings of ASME Turbo Expo 2003, Paper No. GT 2003-38778, Jun. 16-19, 2003, Atlanta, USA. Therefore, the inlet air flow in a so-called “Baseline Mixer” is guided through flow passage sections which twice deflect the flow by 180° in each case before the inlet air is mixed with fuel, which is subsequently mixed by a sequence of a plurality of static mixers, forming a fuel-air mixture. In order to optimize the fuel entry into the inlet air flow with regard to an improved mixing result, a mixer assembly is described in an improved embodiment variant in which the fuel is injected along a flow deflecting contour, by means of which the inlet air flow is deflected by 180°. The fuel injection takes place through passage side walls which bound the flow deflecting contour, in which side walls fuel nozzles are introduced, which inject the fuel into the air flow basically perpendicularly to the flow direction.
The mixer assemblies which are described in the aforementioned article, however, are only suitable for requirements of low burner capacity, especially as the flow deflecting contours at increased flow velocities, especially in regions of small curvature radii, lead to flow separations close to the passage wall, as a result of which flow regions with flow reversal are created, which ultimately lead to inhomogeneities along the flow profile. Furthermore, the double curvature along the air feed passage does not allow any desired compact construction which would be desirable, however, for reasons of an integration into a high-performance gas turbine plant. Considerable mass flows of a homogenous, mixed through fuel-air mixture have to be fed to such plants, which requires high flow velocities at which flow separations are unavoidably established, especially in the region downstream of the passage contours which deflect the flow by 180°, which flow separations, however, it is necessary to avoid.